The technical standard for dynamic olfactometry EN13725:2003 is now widely applied in testing of odours for environmental management purposes. Many laboratories working in this field apply QA/QC systems according to ISO17025 and are accredited under international accreditation, e.g. European Accreditation and NATA (Australia). One of the key elements of the EN13725 standard is the requirement to attain defined levels of statistical performance parameters, in particular Precision under repeatability conditions r and Accuracy A. For the reference odour n-butanol laboratories can establish these performance characteristics in-house, through internal QA/QC measurements. However, the real proof of the pudding is to demonstrate compliance with the requirements in externally organised blind proficiency testing. Proficiency testing for olfactometry has been used since the mid 1980s in the Netherlands and Germany. Currently international proficiency tests are organised by private firm Olfatec, under EN ISO/IEC 17020:2004 accreditation. In 2007 the most recent test was held, with 29 laboratories participating in the extended proficiency test using n-butanol. Of the participating laboratories 12 fully complied with the statistical performance criteria of EN13725. This result confirms that the EN13725 performance criteria are attainable in practice. It also shows that the majority of laboratories claiming to work according to EN13725 actually fail to do so on the key issue of the performance characteristics, a key element of the EN13725 standard. Even more worrying is that among the laboratories that fail to attain the required performance, many are accredited under ISO17025. Of 36 accredited laboratories for olfactometry in Europe only 12 have demonstrated compliance in 2007. This situation may create a false sense of security among users of the data produced, trusting that they can apply uncertainties according to EN13725 while in fact the uncertainty can be larger. It is therefore very important that corrective actions are implemented, and that the accreditation organisations monitor the implementation and also ensure that all laboratories claiming to work according to EN13725 under ISO17025 accreditation actually are able to attain the minimum criteria for precision and accuracy in successive proficiency tests. For users of olfactometry results it must be absolutely clear that a laboratory working according to EN13725 under ISO17025 accreditation will deliver results with a defined and satisfactory uncertainty. Such laboratories must be able to consistently pass proficiency tests for olfactometry. Accreditation bodies are the key guardians of this reasonable expectation..